feat(compliance): prove metric container subsumption end to end

[bokelley]

Summary

Implements #6785 (deferred at triage as blocked on #6618; unblocked since it merged). The container-subsumption rule in available-metric.json was prose-only — nothing pinned independent implementations to the same evaluation. Two halves close it:

Reference seller (server/src/training-agent/): one shared helper (metric-subsumption.ts, 14 unit tests) now backs both surfaces. Notably, required_metrics filtering on get_products did not exist at all for standard metrics (only required_vendor_metrics was implemented — the documented filter was silently ignored); it now evaluates container-subsumes-leaf semantics. get_media_buy_delivery implements requested_metrics narrowing (leaf resolves to its carrier, impressions/spend always included) across totals, package rows, and creative rows, with viewability mirrored to package grain.

Conformance storyboard (metric_container_subsumption, 10 graded validations): the four exercises from #6785, each anchored to normative schema text — container satisfies leaf requirement; mixed container/leaf declarations don't produce empty intersections; a leaf request returns the full carrier object (viewability.viewable_rate AND .measurable_impressions present, clicks absent, impressions/spend always present); and a leaf declaration does not satisfy a sibling leaf (filter-not-fail exclusion).

Verification

• Storyboard in isolated execution: 10P / 0F / 0S.
• Full local storyboard matrix: all seven tenants green; /sales at 126 clean / 559 steps (floor 553) — the new storyboard adds its steps on top of the floor.
• Helper unit tests 14/14; typecheck clean; full schema suite green.
• Patch changeset (additive conformance scenario).

Includes the floor re-baseline commit from #6885 (merge-order safe: whichever lands first, the other dedupes).

Closes #6785.

🤖 Generated with Claude Code

[aao-secretariat]

(non-blocking) Duplicate spread. packageDeliveryMetrics already spreads ...(simDelivery?.viewability ? { viewability: simDelivery.viewability } : {}) three lines up (L12958), before ...byCreative. This second spread of the identical key/value is a no-op — nothing between them mutates viewability. The comment describes real intent (buy-scoped viewability applied uniformly per package), but the first spread already achieves it. Drop the added line and, if the rationale is worth keeping, move the comment to L12958.

[aao-secretariat]

Ladon verdict: Escalate to human review

Escalate — gated path requires human/CODEOWNERS review.

This PR modifies .github/workflows/training-agent-storyboards.yml, which matches the deterministic gated-path glob .github/workflows/**. gated_paths is true and review_decision is REVIEW_REQUIRED (not APPROVED), so decision-table row 2 fires: the hard approval gate is not satisfied and the outcome must be escalate.

There are no blocking (critical/high) findings — the wire-shape logic is sound, the metric-narrowing is schema-safe, and changesets are present and correctly scoped. The only reviewer finding is low (a no-op duplicate viewability spread in task-handlers.ts:12964), which does not block.

Escalation reasons

• .github/workflows/training-agent-storyboards.yml (modified) is under a hard approval gate (.github/workflows/**); requires human/CODEOWNERS review (review_decision is currently REVIEW_REQUIRED, not APPROVED).

Once a human/CODEOWNERS approval lands (review_decision: APPROVED), this PR falls through to a clean approve on its findings.

Why human review

• .github/workflows/training-agent-storyboards.yml (modified) is under the hard approval gate .github/workflows/**; review_decision is REVIEW_REQUIRED, not APPROVED — human/CODEOWNERS review required.
• This PR touches a path under a hard, non-overridable approval gate (.github/workflows/training-agent-storyboards.yml (modified) matches .github/workflows/**) and the current GitHub review decision is 'REVIEW_REQUIRED', not APPROVED. This is a hard gate enforced in code — Ladon cannot auto-approve until a human/CODEOWNERS approval is recorded, regardless of how clean the diff is.